An explosion tore through a crowd of Shia Muslims marking the festival of Ashura in the town of Hangu in North-West Frontier Province.
One report said the devotees were also sprayed with gunfire. Pilgrims reacted by burning shops and cars and clashing with police, a senior official told the Associated Press.
Pakistan's Interior Minister Aftab Ahmed Khan Sherpao said: "Right now we are hearing that eight to 10 people were killed, but these reports are still to be confirmed."
"We thought the bomb was detonated by remote control, but now it appears to be a suicide attack," local police chief Ayub Khan told AP.
"People are fighting. Police are trying to control them. Our priority is to get the injured to hospital, but angry and emotional processionists are attacking police vehicles and even ambulances," an un-named official told the news agency.
The explosion erupted in a bazaar as hundreds of people processed from the main Shia mosque, the official said.
Army troops have taken over the town and imposed a curfew.
The BBC's Barbara Plett said the number of dead could rise further because so many people were injured.
Maulana Khurshid Anwar, a leader of the Shia procession, told AP the explosion happened just as he was about to address the crowd.
Ashura marks the death of the Prophet Muhammad's grandson Imam Hussein, an event that led to the split between Shia and Sunni Muslims.
Biden built a near-half century political career on a foundation of Big Lies and mass deception. They'll surely continue as long as he remains in office.